The print shop asked for 1/8" bleed. Here's what that means and the quickest way to add it.
Shops print on a bigger sheet and cut it down. The blade is never exactly on the line, so if your artwork stops at the edge, a sliver of white paper can show along one side. Bleed is extra artwork, usually 1/8 inch (3 mm), running past every edge, so whatever the cut, it's your design at the edge.
Keep text and anything important at least 1/8 inch inside the edge too, so the cut never touches it.
An AI image or a photo stops at its edge, so there is nothing to extend. The usual fix is to stretch the outermost pixels outward. Mirroring them looks neater on photos but puts backwards lettering into the bleed wherever text runs to the edge.
PrintSanity does this for you: upload the image, pick the finished size, and download the print-shop PDF. It has 1/8" bleed on every side, crop marks outside it, and the trim size recorded in the PDF so the shop's software places it without measuring.