I'd like to use the DEM SRTM 1-arc second (Version 4, 30m) from USGS for Europe. Unfortunately there are some voids. My idea is to fill those voids using the void-filled version 3 (90m) by resampling it to 30m and inserting the missing data in the version 4 DEM.
As I'm new to QGIS I don't know the proper steps. I already got a 30m map by reprojecting the dimensions times three but I'm not sure if that's the right thing to do and I have no idea how to fill the voids afterwards.