Editable Lookups

What do you mean by previous records? Are you trying to keep a running log of who has been in charge of a project? As it stands, your project table is always showing the current team leader which makes sense to me. 

If you mean that some of those projects are old projects and you want to know who the team lead was at the time, then make a separate team lead table and link it to project, don't do a lookup off of the team table. You can also link the team lead table to the teams table so you always have a record of the current team lead. This way you can update the team and the project lead separately and it won't affect the other. 

@FlywheelConsult Yes, you have understood it right - some are old projects. But for the task assigner, it is difficult to remember the Team Leader's name, but it is easy to remember the team name. So is there any alternate solution?

The key is to make the team leaders table. If you're creating a new project, when you assign a team to the project, you can have an automation automatically link the current team leader to the project. In your projects table have a lookup field that shows the current team leader of the linked team then the automation can take that value and apply it to another field that links to the team leader table. This way a person assigning the team doesn't have to remember the current team leader.

@FlywheelConsult, can you help with what logic I can set for the automation to do this? So what my thought is, I have a table with all the team members in it. I will mark the leaders with some tag and then link a particular view to my Teams page. How and what can I automate to auto-populate in the project table?