Lifting the bow at the heel requires a bow hold with a supportive 4th finger, and landing again on the string requires a released 1st finger.
Practise releasing the 1st finger while maintaining the other fingers and thumb on the bow by tapping the 1st finger while the bow is in the air.
When you play in tempo lift the bow with enough speed to allow the note to ring on.
The excerpt is from Forty Variations Op.3 by Otakar Sevcik.
From Violin Technique for Left Hand & Bow – Excerpt From Sevcik Variation 40