Mounting a scope is not as easy as it may seem, it actually requires a lot of practice as well as patience to install a scope mount accurately. Actually the accuracy or otherwise of a shot fired from a gun will depend as much on proper scope mount as it would on individual skill and accuracy of the shooter. The scope ring should be properly fitted on the rifle for further alignment of the scope and the best way to ensure the scope is properly aligned is to try and become self reliant instead of depending on experts that would very much what you could also do with a little bit common sense and loads of patience.
To ensure that your effort does not go vain for want of an accurate gun, choose one you are very familiar with and have ample confidence about its accuracy. The first step for readjustment and remounting a scope would be to remove the scope mount and the scope rings. The next step is rather crucial as it involves zeroing in on the rifle scope. This is a time consuming process and might test your patience to the full but you need to be very meticulous at this stage.
You need V Blocks to properly zero a rifle scope but if you just cannot find them near at hand you can make do with some cardboard cut in a manner that allows you to hold the rifle scope and together with the makeshift blocks align it with some target, preferably a pole situated at least 60 yards away. It would be infinitely better for you as well as your rifle if such alignment is not done with a target only 25 yards away as there are big chances of not achieving proper alignment due to parallax. One should repeat the process of zeroing for both vertical as well horizontal crosshairs to complete the process.
There is one word of advice here.
Though brand new rifle scopes are expected to be zeroed before they leave the factory, it would always be better to check it once to be absolutely sure and try to fix the target as far away as possible as the distant the target the better would be zeroing.
The next step is to fit the zeroed scope into the scope ring and look along the barrel towards the 60 yards target. There is always a possibility that rifle scope would be pointing either right or left of where the bore is as this is a most common error observed in most guns. This is not a serious error as it happens mostly because of slight misalignment of the base with the bore of the gun. Actually, all long time shooters would vouch that rifles bores are rarely, if ever, perfectly centered with respect to the barrel.
The solution to this apparently intractable problem is embarrassing simple. One has to just turn the front and rear scope rings to the right and left as required till barrel and crosshair are aligned with the 60 yards target.