Do they control a light/ceiling fan combo?
The switch on the left is a normal switch and that red wire will go to the fan. That bundle is the feed to the fan/light.
The switch on the right is a 3-way, the black is the switched live to the light. the other 2 wires (red and white) are the travelers to the other switch controlling the light.
You can check this by using a multimeter in continuity mode and check continuity from he black bundle to the white and red of the right hand switch. One line is going to have continuity the other won't. If you flip the other switch which will have continuity will swap. You can then also check continuity between the all the connections of that switch in both positions, which will have the same behavior.
The black bundle would be the live wire. One of those will be going to the same /3 as the travelers I described above.
The 3 way will need to be replaced with another 3-way, otherwise the other switch won't work anymore.
If you don't care about that then you only need to connect from the black bundle to the switch and to the red to the light. and remove and cap off the wires going to the traveler /3