כִּ֛י אִם־מָאֵ֥ן אַתָּ֖ה לְשַׁלֵּ֑חַ וְעוֹדְךָ֖ מַחֲזִ֥יק בָּֽם׃
װאָרום אױב דו װילסט ניט אַװעקלאָזן, און האַלטסט זײ נאָך װײַטער,
Rashi
מחזיק בם means WILT KEEP HOLD OF THEM, as in, (Deuteronomy 25:11) “and layeth hold of him etc. (...והחזיקה ב)”.
Haamek Davar
And continue holding them. Although you have lightened the enslavement, nevertheless, you are still holding them as slaves and making them work.