Once you have your new passport or temporary travel document (if required) you can apply for a visa to return to the UK.
When you apply for a replacement BRP visa from outside the UK, what you actually get is a single journey visa, as a vignette in your passport which is valid for 30 days. You can only use this visa once, which allows you to return to the UK.
Once you have returned to the UK, you will then have to apply for a replacement BRP.