I have a Mikrotik rb3011uias router. I have 2 ISP. My gateways are 192.168.3.3 and 192.168.3.4. I can't change ip range. What can i do? Can you help me plase?

Well, you have the same IP range, but different IP addresses 192.168.3.3 and 192.168.3.4, so it is nothing "special", it is a normal situation with two distinct gateways.

The only issue may be if one of the two gateways is also a DHCP server, if that device goes down you will have troubles as on expiration of lease and new connections devices will have not anymore a DHCP originated IP address, even if the internet connection will be working on the second gateway, but if you have (as usual) the DHCP server on your 3011 and static addresses on the three devices connections that won't be a problem.

The simplest failover setup should be this one:
viewtopic.php?p=1102428
further simplified here:
viewtopic.php?p=1102428#p1102129