Two 3 year terms for Congress.
Maybe you meant three 2-year terms. In any case these changes would require a constitutional amendment, as happened with the 22nd Amendment that term-limited the presidency. The new amendment would have to be proposed by Congress, who are unlikely to term-limit themselves, or by a constitutional convention called by the legislatures of at least 34 states.
In the case of Congress proposing the amendment, you would need a 2/3 vote in both houses.
The president does not have a constitutional role in the amendment process.
Keeps them from campaigning so much.....