You see, this is another problem with this crowd.
NOBODY can give a straight-forward answer around here.

"command-line-options" - proper answer to your question

To turn on coin-control

[click] SETTING
[click] OPTIONS
[click] WALLET
[check-mark] Enable coin-control features
[click] OK

[click] SEND
[click] Inputs...
[right-click (the funds you choose to LOCK or UNLOCK)]
[click] Lock unspent
or
[click] Unlock unspent

If you've already completed your task, good for you.

I'll never understand WHY you people can't just give somebody a straight-forward answer, especially for something so DAMN SIMPLE.
Pathetic !
Sure, the links are good but ANSWER THE QUESTION !