I agree with other posters that spells can take time to manifest, if you are needing immediate results, all I can suggest is diffusing a blend of peppermint and lemon essential oils. This should help clear brain fog.
You could still do some spell work for longer term benefits.
A basic spell would require an orange candle (or white if thats all you have), a tiger's eye crystal, although clear quartz would do, as it's a good all rounder, and your oil blend.
Anoint your candle with the oils, stating your intention, hold your crystal and do the same. Really focus on what your desired outcome is.
You don't have to be poetic or spend too long reciting a pre-written spell. Just state your intention, eg, I am focused, I am attentive, my mind is clear of all distraction.
Obviously you'll need to burn the candle and send the intention out.