I have just started using microtik technology and have following configuration:
2 x RB951Ui-2HnD routers
2 ADSL connections each with one VALID IP in the internet
question is that how can I setup a VPN connection between 2 servers located on each site.
server one is configured as IP 192.168.100.2/29 GW: 192.168.100.1 and server two is configured as IP:192.168.100.4/29 GW: 192.168.100.3 each server needs to communicate with the other one over the internet connections in a secure connection.
I have already setup each router with 192.168.100.1/29 and 192.168.100.3/29 addresses please guide me with further steps which Tunneling should I setup and how should the ADSL modems be setup in order to make things work.

Step1, Try to setup a wireguard tunnel between the two devices. You will have a peer to peer connection which should do the trick, easiest.
Step2 (if required) IF for some reason they need to be able to use discovery or stream, between them to find each other, then use an EOIP tunnel within the WG tunnel.

Since these are older MT models, zerotier is not possible.

Thank you for your reply, can you please let me know how step by step I can set this up, if an online guide is available it will be great

Is it straight IP to IP communications, you didnt clarify how the servers talk to each other?
If straight IP to IP, all you need is a wireguard tunnel
If its broadcast, you can use vxlan over wireguard to do this. It may be easier than EOIP over wireguard.

I have an ADSL modem on each side which has a single public valid IP set on it, on both sides I have a mikrotik router (as mentioned previously). Both servers have a ethernet port setup specially for communication for the other side. one is set to have 192.168.100.102/255.255.255.248 with GW set for 192.168.100.101 and the other is set 192.168.100.104/255.255.255.248 with GW set for 192.168.100.103. each server needs to communicate with other side for SQL Servers synchronization. I can setup port forwarding or DMZ on each modem

Set up a wireguard tunnel and you will easily have the connectivity you desire.
See para F. - viewtopic.php?t=182373