Changing Tempo

I have just joined MuseScore and am really enjoying it. I have transcribed the flute solo from California Dreaming to perform it on oboe at my Ukulele Club at an old folks' home. I need help with:
How do I insert a tempo marking at the start of the score?
Can I slow down the playback from the score so that I can play along with it at a comfortable tempo?

Any help very welcome.

Tina