Routing 1 live ip through different gateways

I have 2 ISP’s (Isp1 & isp2) and bth have given me live ip pools.. Connected on ether1 n ether2 of my mikrotik rb750.
My laptop is connected to ether3 with the live ip and Gateway of isp2.

How do i route my laptop through isp1 without changing the ip settings in my laptop???

Just masquerade your lan pool to another isp.