if the freehub body has slack bearings but the pawls are working OK you have three choices
1) leaving it as it as
2) replacing the freehub body
3) re-shimming the freehub body
If there is no slack in the bearings I would always try lubing it and flushing it first. Even though I have dismantled hundreds of freehub bodies it is still easier to flush and lube them than dismantle them.
If you are going to strip it then first the dust seal has to come out. If this has rubber lips to it, it usually just pries out. If it is made of thin pressed steel then (counterintuitively) the best method for removing it is to bosh it inwards first (using a length of tube) and then knock it outwards. The inwards boshing helps to loosen it. If reusing the dust seal, expect to have to flatten/reflare it, to make it fit again. A new rubber lip seal that fits the majority of shimano freehubs (and a lot of others) is only a couple of quid, so that is a good route too.
If the lockring/cup has two notches in it, the same tool that fits it will fit 95% of other freehubs (both shimano and non-shimano), eg
https://www.ebay.co.uk/itm/Bicycle-Freehub-Body-Remover-MTB-Bike-Hubs-Install-Disassemble-Removal-Tool-/322643815827 If the cup has four notches in, you might get away with a two-dog tool, but then again you might not. The lockring/cup is on a left handed thread, and unscrews.
Beneath the lockring/cup there is a bed of shims. Remove a thin one and replace the lockring/cup. It might take a few goes but you should be able to make it so that there is minimal free play in the bearings. If you are fussy, you can lap the back of the lockring/cup to eliminate that last bit of free play. Note that the reading is correct only when the lockring/cup is tightened properly; whether there is free play or not at other times is irrelevant; if you try and leave it half-tight, the lockring/cup will move in service and will probably self tighten anyway, which will destroy the bearings if you have removed one shim too many.
Note that shims (as well as varying in thickness) come in two main flavours; shimano and non-shimano. They are not the same as one another, being slightly different diameters.
If the freehub bearings were corroded, the result may be a rather rumbly bearing after it has been adjusted correctly. After a few thousand miles it may need to be adjusted again. However IMHO a slightly rumbly bearing with little or no play is much preferable to one that is loose.
cheers
