Hi, welcome to the community.
Does the TP link get a public v4/v6 address in the office network?
Why am I asking this?
If you do not have externally reachable IP, you are not at the step where issues with DNS are to be fixed, but package routing in general.
If you do get a public IP and your office networking staff/policies allows external systems to access the internal one (on port 80/443) you do not need a TP link router in between, similar tools running there supporting DDNS can be run on ubuntu as well (as @Dexter_Kane already mentioned).
If you do not know if your machine is externally reachable: Either get a small Linode (Level1 affilition link) server up and running and try using netcat or curl on the external IP, or some free solutions.
If you want to make it accessible and the ports are locked down: Setup a VPN tunnel with a public accessible machine, see Self-hosted VPN with wireguard as an example 
Note: Make sure your office policies allow running private services, in case someone else gets on that machine from external and does some funny business.