Here is a description of the mission. Credit to the walkthrough guys for the guide.
Main Street Showdown - Innovation Center
We're here at last at the final mission, in three parts. When you start after the cutscene, head right, use the scanner, and then climb up the wall and scoot along the path. You'll fall down and dislodge some bones to rebuild into a ladder. Use Dearing and Grady in combination on the left to dislodge the giant DNA statue, then rebuild it into a hammer to clear the next path. Head through the hatch and smash everything, fixing the checkerboard and allowing the other characters to proceed. Head to the right and enter the dark room, beat off the raptor, and start the generator to distract the raptor. Head down the spiral staircase, cloak past the raptor, build a catapult on the right, and then fix the computer on the left.
Main Street Showdown - Broadwalk Showdown (Part 1)
Head to the right and bust up materials to construct a raptor lever. Open the dark room, turn on the lights, and then use the hatch to get up top, then jump on the amber bricks to take a photo. Next, use the destroyed bits to construct a trike, and then use the scent trail to find a boost pad to the next photo spot. Keep rebuilding the gun, and now you need to shoot at the indominus' mouth when he roars, and then switch to raptors to close in for more damage, the pounce at him. You'll have to repeat this sequence two more times, and then you're done.
Main Street Showdown - Broadwalk Showdown (Part 2)
For the final part of the mission, use the scent trail on the left to the dumpster to build a raptor lever, then build the pieces into a ladder. Dig into the droppings pile up here to find a handle to raise the scissor lift, then send Dearing across to use the control panel here. Scale the rock wall and cut the rope up here to zap the indominus. Then switch to the T. rex and fight the enemy dino. In the next sequence use the raptor lever, then pounce on the revealed spot to get up top. Use the marked zone to jump on the indominus, then use the rex again. After some successful button presses, you'll get the final cutscene.
Also here is a video. Credit to HappyThumbsGaming.