I’ve featured Michael Woloszynowicz twice before this; his Youtube channel is filled with excellent and informative video tutorials. This particular guide is one of his most comprehensive, however.
Michael goes through frequency separations for addressing stray hairs. skin folds and numerous other skin imperfections. Frequency separation in conjunction with dodging and burning is my method of choice for editing portraits and if you’re unsure about either of the techniques it might be worth watching some of Michael’s earlier videos which can be seen here