I woke up totally 'locked' in bed one morning, it took me about 2 agonising hours to get out of bed, get to the computer and get onto You Tube (the home of every fixit imaginable) This 2nd exercise in this video,https://www.youtube.com/watch?v=Jrp1b7FnSqs
starting at 3mins 8 secs helped me enormously.
You just keep doing it , 15 or 20 times every 5 minutes until you can walk without pain, and keep doing it regular until you have full leg movement.
Also if you think the sciatica is going to come on after you did something dubious, then this exercise acts as a prophylaxis in that no mans land time between the physical strain and the sudden onset of the lock down.
However you need to do other exercises to lessen the overall susceptibility for sciatica developing