you need either a chain link breaker or some sort of metal saw, sawzall, dremel with cutting bits, cuz chain off its a pressed on master link
then you need a master link riveter, cut chain to length if its not already, use the spacer tool in the master link press tool, the #1 problem is the master gets crimped too much and then it creates a kink and wears everything out prematurely, good master crimp tools or good mater links come with two spacers you put inside the link so the press can only press so far no matter how hard you crank, so it's never too tight,
if none of this is possible when you crank goa little at a time, remove and look is it mushroomed over, if not go a LITTLE more, repeat till it's just shroomed over, loose is OK, tight is money out your pocket and its so easy to get it too tight, use the smallest wrench you can find to crank the bolt.. bout it really.. inspect both sprockets if they do not look new then replace, clean and inspect axle, bearings, bushings and wheel while you are at it, then re grease everything with a light coat of good heat resistant wheel/bearing grease, you don't grease bearings but do inspect if they are sticky or clunky replace, they should be smooth...
some guys go 520 steel front hard anodized read and maybe a tooth up in the back for better responsiveness, and be sure to remove the packing wax off the chain before install, then lube accordingly, obviously, but the wax, do not forget the wax if it has it.. it gets super gummy if left on