If you create a presentation on a Mac that you want to use again as a model for other presentations, you can save it as a theme. Creating your own theme can be as simple as adding your company logo to an existing theme, or you can design a completely new theme.
You can add your custom theme to the theme chooser, save it as a file to share with others, and install it on your iOS device.
With the presentation open, choose File > Save Theme (from the File menu at the top of your screen).
Click an option:
Add to theme chooser: Type a name for the theme, then click Choose. Your theme appears in the My Themes category in the theme chooser.
Save: Type a name for the theme, then choose where you want to save it.
If you want to install the theme on an iOS device, save it to iCloud. The next time you open Keynote on your iOS device, the theme appears as a downloadable file in the presentation manager. If you want to email the theme to others or to yourself, save it to your computer. You can attach the theme file to an email message.
If you saved a custom theme or if someone sent you a theme, you need to install it so that you can use it in Keynote. Installing a theme adds it to the theme chooser. Skip this task if you chose Add to Theme Chooser when you saved the custom theme.
Double-click the theme file (it has the filename extension .kth), then click Add to Theme Chooser.
You can set Keynote to always open a new presentation from the same theme instead of from the theme chooser. Choose Keynote > Preferences (from the Keynote menu at the top of your screen). In the General pane, select “Use theme,” then click Change Theme to select a theme.
On your Mac, move the theme file to iCloud, iTunes, or a WebDAV server, or send the file to yourself as an email attachment.
On your iOS device, do the following to install a theme from these sources:
iCloud: If Keynote on your device is set up to use iCloud, and you chose Add to Template Chooser when you saved your custom theme, the theme appears automatically in the presentation manager and is identified by a theme badge. Tap the theme thumbnail, then tap Install.
AirDrop: Swipe up from the bottom of the screen to open Control Center, then tap AirDrop. Tap a discovery option, and when the AirDrop message appears, tap Add.
An email: In Mail, tap the attachment, then tap the screen. Tap 
at the top of the screen, tap Open in Keynote, then tap Add.
iTunes or a WebDAV server: In the presentation manager toolbar, tap Locations, tap “Copy from iTunes” or “Copy from WebDAV,” then tap Add.
The theme appears in the My Themes category in the theme chooser.
In the theme chooser, Control-click the theme name, then choose Rename or Delete.
If you’re renaming, type a new name, then press Return.
Custom themes always appear in the My Themes category in the theme chooser, in the order in which they were added. You can’t rearrange them.
After you save a custom theme you created, you can’t edit it. However, you can use it as the basis for a new theme.
Choose File > New, then double-click the theme you want to use as the basis for a new theme.
Custom themes appear in the My Themes category in the theme chooser. If you want to use a custom theme that doesn’t appear there, you must first install the custom theme (see the instructions above).
Make your changes, choose File > Save Theme, then choose an option to save the presentation as a new theme.
You can delete the old theme after you create the new one.