You should be able to get the instructions from the RockShox website, and this is from the Speedgoat blog:
REBA 29ER TRAVEL ADJUSTMENT
For all you asking about changing the travel in your 29er Reba fork, here's where to go on RockShox.com:
Reba Service Info
Page 11 has the travel adjust stuff, but here's the important part: THE PICTURES THERE ARE FOR A 26" REBA, NOT A 29".
For a 29er at 100mm, you will have NO black spacers on there. When set to 100mm, your 29er Reba will look like their "115mm travel (0 spacers)" picture on the far right.
For a 29er at 80mm, you're only putting in one spacer between the white piston-thing and the black top-out thing, so when set to 80mm, yours will look like their "110mm travel (1 spacer)" middle picture.
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