As my previous posts once again.
Wait for a dry warm day.
1:1:2 cement/soft sand/ sharp sand.
Water joints to stop moisture being pulled out of mortar & if any water gets on top of the slab wait for it to dry.
Add very little water in mix to avoid staining the slabs; sometimes there is enough water if the sand is saturated.
Use trowel to place mortar into joints & force down with fingers or similar, several times until joint is full & solid.
Brush any surplus on the surface immediately into unstarted joints with soft broom head, otherwise they may stain the slabs & draw the water out of the mix.
Strike off surface of mortar by pushing firmly down with trowel, so that the mortar is slightly lower than the edge of the paving & on wide wide joints slope up to the middle to a point. Narrow joints can be finished off with the wooden trowel handle or similar.
Fine mist hose spray over paving after a few hours, and then every few hours until dusk, especially if the sun is on it