Howdy the pictures helped. Looking at the roof line at the edge it appears you have a failed roof decking at the overhang( soffit, eve)the area that is bowing down. it is likely a rotten area in the roof decking , plywood, . It also looks like another layer of roofing was installed on top of the existing layer and not a cold roof installed on top of the old roofing. Is the new roofing rolled roofing? Or is it modified Bitumen?
With the problem along the edge of the roof not addressed i would recommend you have this area of shingles removed and repair the decking an if this is the north exposure then have the roofer install ice and water shield at least 36" up slope past the outside wall of the house. Ice & water guard is made to stop ice dams from having water run back under shingles an into the roof decking and into the home. So from the bottom edge about 4' up the slope.
When the roof is opened you may need to cripple a rafter tail and replace some of the facia board too.