Another approach would be to use a very hot iron , pick up one from the local thrift shop, or good will store,and heat the sheeting over a rib at a time. When the epoxy starts to break down, you can pry the sheeting off that rib. The covering iron just doesn't have enough heat to do this job, It gets hot enough, but it to localized to do much good. A heat gun may work, but you stand a good chance of scorching the wood before the epoxy starts to break down.

I would try RCKens method first, but I've never been very good at cutting epoxy that deep.

The last thing, and it may be the quickest in the long run is to sacrifice that sheeting. Cut it up and carve all the wood you can off the epoxy then the heat gun or iron can get directly at the epoxy. Peal it off while it's hot and then lay down a new sheet.

I've done just what your are showing, only on the LE. I used a bit of all methods untill I got a fairly good closure, then I filled in the gaps and sanded things smooth. I will not use epoxy for attaching sheating any longer because of this problem. I now use the carpenters glue and blue masking tape, I wrap the tape next to the ribs on both sides and then use some scrap balsa and clamps and clamp the TE about every three inches. Wood spring clothespins reversed work well for this.

Don