If that is the case then no he cannot unseal those.
If you are talking about his time as President, then perhaps you missed this: White House starts moving Obama's records to Chicago, which means he is being denied access to them by removing them.
Interesting. . .There’s bound to be duplicate files somewhere, even if he moves them—very hard to make government files totally disappear from all archives. I want Trump to release the FBI files on the Clintons, too. . .
Having worked in the Ford and Reagan Presidential Papers, it’s worth noting that these are ONLY the official papers of the presidential administration. They do not include anything before taking office or after leaving office.
In addition, the papers of subordinates that are NOT policy related-—unless specific direct copies are made—reside at private collections in other libraries. For example, “Judge” William Clark, Reagan’s key advisor for yrars, has his papers at the Hoover Institution.