I'm changing indoor service panel 100amps I have 4 wires coming in but only see 3 places for the large wires

What do you mean by indoor service panel?

Do you mean a 240V sub panel?

Your Main Breaker is probalby out at the meter, and not in this panel.

You need to purchase an accessory equipment ground bar and bolt it to the panel using machine thread screws, and connect the green or bare equipment ground wire, one of the four wires,to it, along with any other green or bare branch circuit equipment ground conductors.

The neutral bar must remain insulated, do not connect the bonding jumper, or install the green screw.