Step one; Go to back eraser When you open the app it should look something like this
Step two; open up a random picture[for this I used wattpads cover size 512x800]
Click on the plus sign>camera roll>then click on your picture
Step three; Start erasing it
Step four; save background as a png
Click on the box with the plus sign>click on PNG transparent background
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I hope this helped you with something. But I don't know if this made sense or not XD. You use this transparent background for making transparent fonts. If that doesn't make sense I'll make a tutorial about it.