Limiting and a good clipper too.
Run a couple of limiters in series so neither does too much work.
Or better, 2 compressors, 1 optical, 1 Electro FB, then a limiter.
Or even better, use mid side processing to split the mix and then process the mid and side each wth it`s own set of series compressors and limiters.
Or even better.......

Get a good mastering engineer to do it properly.