There's nothing I can find on where they specifically intend to get the funding, but $100M is not a lot of money in a $2T budget. My bet is that it's money already allocated that was either not designated for a specific use, or it was meant to be paid out, but got halted after the Oct 7 attacks. The US State Department lists some possible sources for funding in general
Since April 2021, the United States has provided over half a billion dollars in assistance for the Palestinians, including more than $417 million in humanitarian assistance for Palestinian refugees through UNRWA, $75 million in support through USAID, and $20.5 million in COVID and Gaza recovery assistance.
The U.S. government plans to provide an additional $75 million in economic assistance to the Palestinian people this year. Additionally, the United States is also providing $45 million for programs to support the security sector including important improvements to the rule of law.
In addition, $100 million directed to the Nita M. Lowey Middle East Partnership for Peace Act (MEPPA) for the first two years of a 5-year commitment will strengthen people-to-people engagement between Palestinians and Israelis to create the conditions for lasting peace.
I would assume some of these funding sources are still available to pull from.