I have found my manual belt tensioner and I used a socket wrench to loosen the bolt holding it in. But it was so tight that I broke my wrench trying to loosen it and have left my old belt on there since.
My car has 58000 miles.
My car has an automatic transmission.
You were correct to try and loosen the tensioner pulley bolt and then loosen the side adjusting bolt to loosen the belt for removal. If you broke the tool you used to try and loosen the pulley bolt then you may have to purchase a good quality tool or have someone do it for you. The belt is very simple to change once you remove the right tire and inner fender cover to access the belt and pulley. I recommend you contact a mechanic, such as one from YourMechanic, to come to you and change the belt for you. This way you do not break any more tools and so you know that it is done correctly by a qualified mechanic.
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