It appears that many folk are entitled and have not yet claimed. (most will have received their cheque automatically, but some can slip through the cracks 
)
Here is a link:
all you have to do is put in the 13 numbers of your Numero Fiscal and the simulator will tell you whether or not you are eligible for this financial aid.
https://chequeenergie.gouv.fr/beneficiaire/eligibilite
EDIT: under āJe connais mon numero fiscalā
you click onto OUI and it opens a line for you to enter the 13 numbers
and it then, asks you to prove you are Not a Bot by entering whatever you āseeā in the box and then clicking āContinueā
