Gen 2:1-3
Thus the heavens and the earth were finished, and all the host of them. 2 And on the seventh day God finished his work which he had done, and he rested on the seventh day from all his work which he had done. 3 So God blessed the seventh day and hallowed it, because on it God rested from all his work which he had done in creation.
God rested on that particular 7th day. It doesn't say God rested every 7th day, any more than he created plants every 3rd day or fish and birds every 5th day.
There is no indication that Adam and Eve rested on the 7th day. Indeed since they were in Paradise there was no work for them to do. It was not until they fell and were expelled that God says to Adam:
"Because you have listened to the voice of your wife, and have eaten of the tree of which I commanded you, 'You shall not eat of it,' cursed is the ground because of you; in toil you shall eat of it all the days of your life; thorns and thistles it shall bring forth to you; and you shall eat the plants of the field. In the sweat of your face you shall eat bread till you return to the ground, for out of it you were taken; you are dust, and to dust you shall return." (Gen 3:17-19).
God didn't tell them to rest every 7th day.
Moreover the writer of Hebrews makes a point that God’s work was completed in the six days and so God’s rest is continuous.
“…although his works were finished from the foundation of the world. For he has somewhere spoken of the seventh day in this way, "And God rested on the seventh day from all his works." (Heb 4:3-4).
There is no cycle of God working for six days and resting every seventh day.
There is no mention of anyone keeping a sabbath until Ex 16 when the instruction was given to the Israelites in the desert. And it is clear they did not understand the concept. In Ex 20 God reminds them about keeping the sabbath, and again in Ex 35 God reminds Moses about keeping the sabbath, and again in Lev 23.
There is no evidence whatsoever in the Bible that anyone kept a 7th day sabbath before Ex 16.