I've tried the following:
— followed the link to How To: Completely Erase the ROM of an EMS 64m USB Gameboy Cart, but it doesn't seem like my cart is an EMS 64m nor do I have a cart reader. So this doesn't seem like a solution, right?

— I cleaned the cart and Gameboy pins with 91% isopropyl alcohol.

— As suggested in the LSDJ manual "Try removing and re-inserting your cartridge about thirty, forty times.", also to no avail.

Is there a way to check the battery to see if it's truly dead? If it isn't dead can I use any old 3V coin cell as a replacement?

Any tips or guidance on bringing this cart to working order would be much appreciated.

Here's photo of the actual screen.

This is the front of the cart

Here's the back of the cart

2.11.1 Total Memory Reset
By pressing SELECT+A on the LOAD/SAVE FILE button, you can choose
to reset all memory. This can be useful if your memory somehow gets
scrambled, or your cartridge start to behave strange in other ways

or go into your cart programmer and click on erase or format or whatever it might be

Ok so the title pretty much sums it all up, i got a used LSDJ cartridge and I want to start with a blank canvas, how do I do that?

go to the project screen, go to load / save song, go to "delete", and then delete the songs one at a time.

all the answers to these kinds of questions are in the manual.