Proper roller ski technique requires sharp tips, the best are specially made tips for roller skiing as they are built to withstand the extra stress of poling into asphalt. The local ski stores stock roller ski tips. If you are going to change the tips from the snow baskets use hot water in a bucket, do not attempt a heat gun, after a while the heat should soften the glue and you can carefully twist the tip off. Use a hot glue gun to glue the roller ski tips on.
If you are using previous roller ski tips make sure they are extra sharp. Use a diamond file, see picture, working both sides of the tip. The diamond files can be purchased at local hardware stores like princess auto. It’s a good idea to spend some time doing this before you starting to roller ski each session. Other information can be found on the web about using a grinder for sharpening.