The easiest way to create an album cover is by uploading your song through the Songs page.
Once you upload the song, you'd be taken to a page that hosts the details of your song - including the waveform, lyrics, and any clips you've created with it.
You can click on the squirrel at the upper left-hand side, next to the title of your song.
From there, you'll see a pop up box with a prompt box and a style dropdown. Enter your prompt, select a style, and then select Generate.
After that, you can click on the album cover and then Right Click + Save As to save your new album cover.
Another way to create an album cover is by selecting a model and generating a text prompt. You'd want to ensure that you lock in a 1:1 aspect ratio and then you would Right Click + Save As for your preferred image.