SketchUp can export its own drawings to several 2D graphics image formats including the BMP. You can find the function at File → Export. Just be advised that this export function will only export one view of the 3D model, so when you would import this file back to SketchUp you wouldn't get the original model back. If you want to convert whole mode, use one of the 3D formats instead.
Convert SketchUp graphics to Standard Windows bitmap image.
We have found 2 software records in our database eligible for .skp to .bmp file format conversion.
Microsoft Windows software - convert skp to bmp on Windows
A 3D general-purpose modeling program
Convert from skp file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned skp to bmp. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert skp to bmp on OS X
3D modeling application for Mac