need to reinstall iphoto after upgrading to Mojave

iphoto seems to have disappeared and I may need to reinstall it. How do I do that?

Has iPhoto '11 disappeared or is the Photos missing? You mention iPhoto, but are asking in the Photos for Mac forum?

• If iPhoto is missing, check if it is still in the Applications folder. If you can find iPhoto there, drag it back to the Dock. If iPhoto is not in the Applications folder, open the AppStore and check the Purchases history. In Mojave, you can see your past purchases, if you click your account name in the lower left corner of the AppStore window. Then try to reinstall iPhoto from the list of past purchases.
• If Photos is missing but you can find it in the Applications folder, drag it from there to the Dock. But if it does not even show in the Applications folder, you have an incomplete installation of Mojave. Photos is a part of the system and cannot be installed separately. In that case boot your Mac into the recovery portion and reinstall MacOS X on top of your current systems, see: About macOS Recovery - Apple Support