AHC: Skylab reboost mission between 1974 and 1979

What would it take for NASA to launch a mission to Skylab to reboost it into a higher (but still accessible by the shuttle) orbit sometime between the end of Skylab 4 and when it’s orbit decayed and it reentered the earth’s atmosphere in 1979?

Would the reboost mission have to be manned? Does NASA have the hardware to do it?

What OTL missions would have to be sacrificed to accomplish this?
 
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