Is there a way to restore the default form on a sharepoint list using a customised list?

[Victoria Symons]

I have published a PowerApps customised form to a SharePoint list believing I could switch back the list back to the default form. I should be able to do this. However in list settings > form settings, the settings are missing. I have 'The list does not have any valid content type' instead. 

This is problematic because this list is live and the PowerApp is nowhere near finished yet. I could really do with switching it back. Does anyone know how to restore a default list form in SharePoint or how it might have got deleted? It was there before I created the PowerApp. I have not intentionally deleted it. Thanks so much. 

[#2]

Tray to grab the URL that allow to change the list form setting from another list and see if you can change the setting in the customized list

[#3]

I have the same issue. Most posts related to similar problems that I found on the web refer to the list settings which I do not have access from the List Web Application. Very frustrating. I feel like an Apple user using an Android application. Sigh!

[#4]

@JPhReid 
I'm sorry to say I never managed to resolve it. I just had to work quickly. The only thing that occurred to me was that my list was on a classic site, all be it, in the modern view. Spoke to Microsoft at the time and they didn't know why it had happened or a way to get my old form back.