Umap: filtering objects by location

[newbie]

Dear all, I’ve been using Google Earth for many years in order to collect interesting points (pins) all over Europe. Now it’s time to move on to umap. I am a newbie. Though I managed to import my 3000 points through KML, but layers / folders are gone.

My question: How can a select objects / points in a specific regional area (say Belgium) and allocate those to a new Belgium layer? It is so many objects that I cant select them separatly and put them on a new layer.

Thanks, nepo