I included a link to the instructions, but they don't appear to be very helpful. I am pasting in some Amazon comments from someone else that shares you frustration with the device, he ultimately provides some info that you may find helpful:
This is by far, the worst designed Chinese contraption I've ever had the displeasure of owning. I needed one in a hurry, and realize when you buy "China" that you take your stress level into your own hands......BUT, I gave it a shot. The bolt holes are drilled off mark, leaving you to bend the item into shape as you go......and the most important aspect, that is the tape roller assemblies, are so far from a proper design spec that it's nearly useless. I had to literally refabricate the assembly to get the tape to roll off evenly (by shimming the bushing AND the shaft, which is also improperly designed).....SO sloppy it's a joke, but I wasn't laughing.....the plastic tape roller mounting hole is SO over-sized that it's almost IMPOSSIBLE to get a straight and smooth distribution of your tape. FINALLY, after nearly 2 hours of tinkering, it worked "OK"....for just a LITTLE MORE QUALITY CONTROL, they could have avoided the design fiasco.........Parts were also missing (second tension spring, and 2 roller clamps).......TERRIBLE quality..........Brother, do I miss USA made goods. I'm a 45 year body and paint man......I believe I know 'what of' I speak.............This thing is CHEAP as a purchase price goes, but you'd better be ready for an elevated frustration level based on it's overall POOR quality. Period. If you're looking for ANY kind of precision in your tape rolling, FORGET IT.