The first thing to do is find the water source and correct that. Next, poke the wood with a pick or flat lade screwdriver. It could be dirty and not be rotten.

No active leak and it is rotten.

It looks like surface deterioration on the wood, and it doesn't affect anything structural. If there are no signs of water issues and this will be located in a concealed space, you can use a Rot repair kit just to prevent further deterioration issues.

Thank you so much GN Builders LLC. Any suggestions?. Looking in Home Depot and see a lot of different options. Something like am of these would be ok?  Varathane 16 oz. High Performance Wood Hardener 340229 - The Home Depot https://share.google/HxiKVZyf0JBrhWPwE

DAP Plastic Wood-X 8 oz. All Purpose Wood Filler Repair Kit 00596 - The Home Depot https://share.google/cEqISdxXSYJqiSFX0

I'm not sure what they sell in HD, but I used to get this product in a 1/2 gallon size on Amazon. For something small, as you have, you can get it in a pint. Here is the LINK

This one is also good, sold as a repair kit LINK

Just wear gloves when you use this stuff. The kit comes with a bottle that has markings on it. Just follow the instructions, mix it right in the bottle, squirt it on the area, and use some cheap blush to spread it over the area, and that's it, very easy to use.

Good luck.

Thank you so very much!!!!!!!