If you're on your own, flaking a boltrope headsail is a very difficult operation.
Consider getting your sail modified, with slugs (eg Kiwislides) in front of the boltrope. Now when you drop the sail, it's like a hanked-one sail: you can do a rudimentary flake without disconnecting the luff from the foil.
I don't know of any safe way for a person on their own to change a boltrope headsail at sea in a breeze, unless the sail is fitted with suitable eyelets and a downhaul.
Jib Downhaul & Stowage ?
With two people, flaking is easy if it's done methodically. The key thing is for one person to drive (usually the person at the luff), and person at the other end to mirror exactly what they do.
Person 1 is facing aft. The foot of the sail is inboard and the sail lying along the starboard side of the foredeck and cabintop (say). They grab the luff at the first fold with their left hand. Person 2 mirrors this with their RH where they estimate Fold 1 would intersect with the leech. Person 1 hauls forward with LH on the fold line, as Person 2 hauls aft.
While maintaining this tension (this is the key to flaking quickly and well) Person 1 grabs the luff with their RH in the right place for fold 2. Person 2 mirrors this on the leech with their LH.
Both maintain their equal and opposite tension on fold line 1.
They haul Fold line 2 across into position whilst pulling evenly against each other, Person 1 dictating where the luff ends up. Once it's nearly in position it will become clear who needs to shift their Fold 2 hand.
Once Fold 2 is in position, maintain tension by pulling against each other, let go of Fold 1 and reposition that hand for Fold 3.
As before, maintain the tension along Fold line 2 until Fold 3 is in position and tensioned.
Each fold should line up with the one underneath: Fold line 1 with 3, 2 with 4 etc.
When it's flaked, each person folds up a short section towards the other person, continuing until the two resulting rectangular slabs at the midpoint can be folded together to form a 'brick'