How can congress exert control the executive branch

Congress can influence or exert control of the Executive branch in a number of ways.

The most important is that Congress sets the legislative agenda, so in a way, Congress gets to set the tempo for what is covered.

Congress, via the Senate, also has the ability to approve or reject Executive branch nominees.

Finally, the House has the ability to subpoena and investigate the executive branch to ensure that they are doing everything correctly.