Cannot Return to Mac from Bootcamp

Trying to install Windows 7 in my MacBook mid 2012, I got the message, “Windows cannot be installed to this Hard disk Space. Windows must be installed to a partition Formates as NTFS. “ There was a button “format”, so I clicked it and could proceed, but installation failed. Believing that the “Format” button did not work, I searched the internet for solution and found one, quote: “Select each partition beginning with Drive 0 Partition 3 then click Delete until there is only a single unallocated disc. Select the unallocated disc and click New , this will split it in two, select the Primary partition then click next to begin the install.” The person who asked the question replied that it worked. So, without searching further, I followed the advice.

I deleted the partitions 1 & 3 ( of course I was warned, but thought stupidly that I had no choice) not daring to delete the main Mac volume. It did not work as the man described above. The button “New” remained greyed out. So, as there was nothing else to be done, I clicked “Format” again and proceeded to set up Win7. It failed again. Worse, I must have deleted the program to return to Mac by restarting with the “Alt” key pressed. There is no Mac disc icon, so I cannot return to Mac!

Could somebody advise me, whether it is possible to restore the lost program to choose Mac and Windows? And if possible how!

As for the Windows installation, I managed, so the “Format” button worked, but currently my MacBook is just a Windows 7 laptop!

Your good advice would be very much appreciated!