One of the oldest methods for cutting curves on inside corners is with a tile saw. After you mark the paver, take the piece to the tile saw and place it on the tray. You can maneuver the paver on top of the tray and push it into the saw at various angles to trim the edges off, eventually ending up with a rounded edge that will slide into your inside corner.
Angle grinders can achieve the same thing as a tile saw, although the method is different. The blade of the angle grinder is pressed down into the face of the paver just slightly to the waste side of the curvature and the blade moved along the contour of the corner. As you press downwards and make multiple paces back and forth across the face of the paver, you will eventually cut through the piece along your mark.
If you are dealing with only a slight curvature and you have rough pavers, such as flagstones, you can use a hammer and chisel to knock the edge off pieces to give them a rounded contour. It takes time and physical effort but if you work slowly you can chisel away sections to a fairly accurate perimeter, after which you can install the paver directly into the place snugly.
Pie-shaped wedges is another method of cutting pavers into inside corners. It is not as popular as simply contouring the edge of a paver, but it is still seen in some areas. You cut multiple pieces into pie-shaped wedges that you install in a fan or sunburst pattern that bends around the edge of the inside curve, allowing you to keep a precise and controlled turn for tile-like paver installations.