There is only one way to "regenerate health" in Tanki X and that's by collecting these repair kit supplies.
Each repair kit will restore 200 armor points per second - the repair process is not instant - and reduces the duration of burning and freezing effects, if you have any, on your tank.
They will usually spawn periodically in fixed locations around the map but you could also spend diamonds to buy additional kits. Just make sure you're the one to collect it when it drops.
These crates are incredibly helpful especially in 1-on-1 situations. After all, a repair kit can almost be equated to getting a new lease on life without going through all the dying and respawning processes.