Although there are many way to modulate and connect the two hymns, here is what you can do (modulation from C major to D flat major, done on the secondary manual):
1. After your 1st hymn, play its last line in F minor (perfect 4th upward).
2. Then play the same line in D flat major (major 3rd downward).
3. Play the 1st line of the 2nd hymn in D flat major.
4. Play the last line of the new hymn in D flat major.
Try this exercise with any two hymns of your choice today and post your time to comments (feel free to transpose the hymns in order to adjust the key relationships).