On a B1/B2 combined visa how do i go for a B1 business trip

[dslm65]

I was given a combined B1/B2 visa.

I visited the US a couple of years back.

Now I have a short 2 month business trip coming up.

Do I need to apply for a B1 visa OR travel to the port of entry and provide documents supporting B1.

My next trip could be a tourist visit will my B2 visa stay valid for that trip ?