There is no way to prevent a specific stock from being lent out if you are currently participating in SYEP. The program is entirely managed by IBKR who, after determining those securities, if any, which IBKR is authorized to lend by virtue of a margin loan lien, has the discretion whether any of the fully-paid or excess margin securities can be loaned out and to initiate the loans.
If you wish to restrict some or all of the stocks from being lent out, you would need to opt out of the program. To do so, please see: How does one terminate Stock Yield Enhancement Program participation?