This very small, but extremely useful tweak is designed to make the mechanics of swimming for the version of your minecraft 1.12.2 as similar as possible to version 1.13 (but to use it you also need to press Ctrl).
How to install BetterSwiming Mod
- Download and install Minecraft Forge
- Download mod
- Do not unzip it, copy to C:\Users\User_Name\AppData\ Roaming\.minecraft\mods