Xv535 cam chain jumped one tooth on cog,tensioner is fine ,so how did it happen,and how can i fix it

If all cogs and bearings are fine and that the chain tension is at specification then it should not be possible for the chain to ever jump a tooth. The amount of movement required by the chain to jump a tooth is considerable. I have only ever seen this as a result of an oversight when re-installing the chain after doing upper cylinder head work such as gasket replacement. Some models of vehicles with V6 engines that integrate the timing belt with driving the coolant pump can sometimes jump a tooth if the pump bearing fails. I would again check the chain tension once the timing chain is re-installed, even without tools you should be looking for a chain that is obviously taught. Not piano wire taught as this will lead to early failure but certainly one without any slackness or rattle. I have little experience of bike engines but the principles are the same