It can be adjusted, one end at a time, and not sure why they told you slide would have to be adjusted. Hard to explain without pictures. Basically remove the awning end from the bracket (the one on the outer slide out wall), being sure to hold on to it where it doesn't unwind, wind a few more turns in it and reinstall. Repeat on other end of slide awning. Might have to extend slide a little for removal from bracket. Depends on model and how it's secured.
John and Rebecca Dickson
Emma-7 / Little John-5 / Iva-1
Full Timing Again, Rev B
2013 Ford F-350 Lariat CC LB PSD
2015 SOB TT - With OC's Awning Poles (#8)
At least in Heaven, RVs will be perfect, and I won't have to keep fixing them.