فَلْيُكْرِمْهُ can be read in three functional parts:
فَـ — links the consequence to the condition.
لْيُكْرِمْ — gives the instruction “let them care for.”
ـهُ — “it”; its antecedent is شَعْرٌ (“hair”).
Correctly identifying a pronoun’s antecedent prevents a misleading translation. The command concerns appropriate care for the hair, rather than a separate, unnamed object.