Meltan Fixer
From Pixelmon Wiki
Meltan Fixer is a Pixelmon sidemod that temporarily fixes an issue with Meltan not spawning in 7.0.6, and another where it will not evolve. This mod will not run on older versions, and will not do anything on newer ones.
To install Meltan Fixer, simply drag it into your game or server's mods
folder, and then restart it. It will run in the background and fix these issues silently.