To remove a jam from your "My Jams" list:

Endlesss Mobile

Open the jam. On the page where you can see the chat, tap on the name of the jam at the top of the screen. Here you can find the "Remove jam" button.

Endlesss Studio

With the jam open, click on the gear icon in the top right to open the settings menu. The "Remove Jam" button is found near the bottom of the list.

You can rejoin the jam in the future using a valid invite link.