Hmm, the same screen should have buttons to spend... Are you playing on Android? If so, there might be a bug related to that, and I can fix it. If not, I'd love to see your save file in case something is terribly broken :D
If it's on Android, then there's a bug that's preventing those from showing up. Hmm, well, the good news is that I'll be fixing the issue for the next update. The bad news is that I'm still working on that update, so it'll take a while before it'll go public. I'll probably release the beta on Patreon/SubscribeStar this week, so it'll be public and on Itch a few weeks after that.