US Treasury Bill will Mature on Thurs, Oct 22 - how to re-invest part of if before Maturity

I purchased 13-week Bill on US treasury. It will mature Oct 22. But I want to re-invest part of it today, Oct 18.

When I log into my Treasury Direct account, there is option to edit my security, i.e. to reinvest and specify how much to re-invest. Instead, it has status, "Pending Maturity"

I sent an email, but I just wanted to know my options before the Treasury Dept opens tomorrow, i.e. Monday morning.

How to re-invest part of my investment instead of it all maturing on the 22nd.

Please help.