On the back of your watch you will find the Omega reference number - it´s a unique number for this particular model. On the watch it is listed as "136016" but the correct format is 136.016. On earlier Omegas you will have to look at the inside of the caseback for this number.
Start by googling "Omega 136.016", and you will find information and pictures. The Seamaster Cosmic is not the most popular model of the late sixties (not really sure why), but it´s great quality and due to the unusual design of the back, it´s very comfortable to wear.
You may also want to have a look in the Omega Vintage database online. When you enter the ref. number as search criteria, you need to add an extra zero after the dot, like this: "136.0016".
You should be able to come up with this:
https://www.omegawatches.com/planet-omega/heritage/vintage-details/25949/
Best regards