Hello.I have a problem that I noticed about 2 weeks ago I haven't been able to solve it myself.I have a Bachini bike with Shimano gearshifter and dereilleur and 7 gears.However whatever gear I try to put it on it always puts it one gear
higher.In the pic I've put it on 4th gear yet the chain is on 5th gear.I've tried taking off the chain and putting it on the correct gear,but it always puts it back on the higher one.Can I fix this myself without some special tools?