It's usually possible to get a 90 degree machinist's or sharp pick tool in the groove and pry the end of the snap ring out. I've done it more than once that way, have a pick in one hand and a screwdriver or knife blade handy in the other so that once the end come out of the groove you can pry it upward a bit. Just keep working the pick around the edge of the ring until you can get enough of the end to get hold of with a needle nose plier.
Some times a new seal is thick enough to make it difficult to push the circlip or snap ring down far enough to engage the groove. A good trick when reinstalling the snap ring on top of the seal is to slip it in place above the seal and then use a piece of ABS pipe big enough to slip over the fork tube. You can split the piece of ABS, stick the two halves back together around the fork tube and use a couple hose clamps to hold it together. Then just use slide the tube down on the snap ring and pop it a couple times using the piece of ABS pipe like a slide hammer. The clip will pop nicely into the groove then all you need to do is to check the ends to make sure they are fully seated.