ABS Fare sold with Thalys for about 7euros would let you take any train Bruges to Brussels within 24 hoursof your Thalys Brussels departure - could spend night in Brussels but from Bruges better to buy Bruges-Antwerp-Amsterdam for prices as low as 36 euros as above.

Pal, if he has already bought his Thalys ticket from Brussels, there's no point in saying he should get an ABS ticket.
Anyway, if I book Thalys there is no 'ABS' option; I choose the station of departure, and get a rate based on that. So I choose Brugge as departure point, rather than ABS'. But it doesn't matter, since the OP already has Brussels-Amsterdam Thalys tickets. In which case he just needs a local Brugge-Brussels Midi ticket in addition to his Thalys ticket.

Anyway, Brugge-Brussels-Amsterdam is not a bad option on Thalys. Brugge/Brussel takes an hour, and trains are frequent. Brugge/Antwerp is 1,5 hours, less frequent trains.

And fares on Thalys vary wildly from day to day, even between trains at different hours of the day.

There is no way to add on ABS fare now? did not note OP had booked ticket

Will the IC train from Bruges to Brussels be free that day, is there anything will need to do other than show proof of the Thalys booking..... i hope i explained that clearly>

No - unless you bought the ABS fare at time of booking - Tulips says but I'd still try to add it on somehow - then you could hop any IC train to from Bruges without going to ticket window.

No need to go to a ticket window. Just buy a Brugge-Brussels Midi ticket online, have it on your phone to show the ticket collector. It's valid for any train that day.
It costs 14 euro. Wether you buy it today or on the day.

ABS fare is 7 euros so not really much different.

thalys fares are all over the place. Sometimes cheaper than a regular IC. Sometimes 3x as much. Maybe the international version is different, but i cannot book an ABS fare; i just put in the station I'm leaving from, ie Brugge to Amsterdam, and Thalys gives me a fare. There's sometimes a difference of 50 euro one way between different trains the same day. The Belgian rail site is easier to use than Thalys' site, and gives you all the options and prices.

Bruges to Amsterdam if I put in Thalys I get a lot of 36 euro fares and I believe that includes the ABS fare.