Standard ways of freeing a stuck clutch are:-
1: Start the engine, ram it in gear and hope that the clutch will break free.
2: Find a straight quiet stretch of road, some nerve and enough people to push it to the start position. Put the car in gear and use the man power to bump it until the clutch frees off - sometimes!
3: Alternatively, park the car against a high curb with the engine running - bodies are needed to reach this position - and ram the car into gear. Dexterity is needed on the footbrake if the clutch does not free off and the car mounts the pavement.
Some years ago I was shown an alternative method which requires only one person and involves no risk, but perhaps a little more time. The procedure involved was as follows:
Find a suitable flat firm area - the drive would be ideal. Chock the front wheels so that the car cannot move. Now jack up ONE rear wheel. Place sufficient large pieces of timber under the axle on the side that has been jacked up so that when the jack has been removed the wheel is still be clear of the ground. Remove the jack and rock the car to ensure that the timber is supporting the car safely, and check that the wheel is clear of the ground. With the handbrake on, start the car and allow it to run until the engine has reached full operating temperature, and then switch off the engine.
Engage the HIGHEST gear, fifth or fourth depending upon which gearbox is in the car. Release the handbrake. Start the engine in gear and allow it to idle (this is the reason for getting it to operating temperature before starting the procedure). As one wheel is off the ground, that wheel will rotate on its own due to the differential axle.
Often the vibration from the drive train rotating together with operating the clutch pedal is sufficient to free the clutch. Should this not release the clutch then stronger measures are necessary.
Pump the brake and clutch pedals simultaneously in a rapid on/off motion several times without allowing the engine to stall. It is NOT necessary to rev the engine. This, in my experience, releases 98% of seized clutches. Check the full range of gears, particularly reverse, for operation. Switch off the engine and apply the hand brake...
Jack up the car and remove all the blocks. Remove the jack and chocks under the front wheels. With the engine running, gently operate the clutch in conjunction with the gearbox to confirm that all is well. Take the car for a test run to 'bed in' the clutch.
This may seem a little long winded, but at all times you are in complete control of the situation and no-one is going to get hurt.