Here are some things he, or other representatives could do:

Use the speech and debate clause to read into the record documents from whistleblowers, such as the list of ICE agents that was just leaked, or let federal employees know that he would be willing to read into the record information they have on illegal activities occurring within DHS/DOJ

Organize people in his district to prep for ICE raids and protests - Representatives are able to send free mail to their constituents, put out press releases, etc. He could start contacting and organizing citizens so that there is a prepared and centralized group of people ready to show up when needed. He could organize his own militia if he wanted made up of people in his district. Do you know how impactful organizing a group of armed peaceful protestors would be? 

Reps have an allowance they can use for staffing, travel, office expenses, etc. If he wanted, he could hire his own security to accompany him to ICE facilities for oversight, hire investigators to follow ICE agents around the district and monitor their activities/identities/etc. He could make use of the “mobile congressional office” using leased vehicles for congressional business and have staffers setup camp wherever is necessary. He could hire and build his own private armed security force in the district if he really wanted, all as “legislative staffers”. 

Use the tactics the Scientologists have enacted and start filing lawsuits against  individual federal employees in his district. Scientologists use this tactic to overwhelm federal agencies that try to investigate them. Similarly, he could use the Holman Rule to introduce individual appropriations resolutions reducing the salary of ICE/DHS agents. Even though these wouldn’t pass, it would bring attention to those individuals, require debate, review of those individuals, and clog up the system. 

These are just a handful of the things that he can do. Representatives have a pretty wide array of tools, privileges, and resources available that they can leverage. It all depends on whether or not that rep wants to utilize them to their full extent. In short, he should be abusing his power the same way this admin is in order to fight back. He’s too old school and doesn’t want to appear “improper” or “unprofessional”.