It seems to be really easy to make such a DIY ring holder :)
Links:
DIY Ring Holder (What a cute idea for organizing rings or brooches. According to a pinner, “DIY Ring Holder: Since all the tutorials I found meant a LOT of cutting, rolling and gluing, I decided to do it MY way. Repurposed materials: a cheap sponge, a discarded tin & fabric scrap. Actually used my fingers to tuck the fabric instead of the knife as shown. Didn’t bother with glue. Formula for fabric size: D+D+W+1″= fabric Width by D+D+L+(number of slits X 1″)+1″= fabric Length.”) (englisch)
=> unfortunately I haven’t found the original instruction