It's about what is used for the tunnel itself ('outside the tunnel') and what is transported within the tunnel ('inside the tunnel').
A "TCP meltdown" can occur when TCP is used for both outside and inside traffic. Both TCP instances don't know about each other and may compensate for the exact same temporary problem. Due to their stacking, measures add up, overcompensating the problem. This can easily lead to a resonance where the overall performance is suboptimal.
The best solution is to use the non-compensating UDP protocol outside the tunnel. UDP performs just like IP, so traffic flow is fully controlled by a single TCP instance, if used inside the tunnel.
Can UDP traffic be transmitted over TCP ports on OpenVpn to avoid the TCP meltdown
That's isn't possible since TCP and UDP are different protocols. Their port numbers use the same range but have no relation whatsoever (on the transport layer - a specific application layer protocol may use the same port numbers for both TCP and UDP though, like DNS).
The solution is to either use UDP inside the tunnel - that is controlled by the application(s) however and cannot usually be selected at will - or use UDP outside the tunnel, which you can do by setting up the VPN gateway properly. By default, OpenVPN supports both UDP and TCP for the tunnel, with preference to UDP.