Washing your knits too often could damage the piece. Merino Wool, Alpaca, Cashmere, and Mohair don’t need to be washed as often as other fibers. They are naturally odor resistant, stain-resistant, and easily bounce back to their original shape after resting.

If desired, you could freshen up your knit by hanging it outside and spraying some linen water on it. The linen spray will add a light scent, whilst removing undesired odor and dirt. and keeps sweater-destroying moths away. Just a few sprays are needed, let the mist dry and you’re all set! You can buy linen waters from brands like LA Brucket and Marie Stella Maris.

If the method above is not giving you the result you’re looking for, you could wash your knits on a very low temperature (30°C), never cold wash.
the steps are simple:
 
1-Fill a basin with water on a very low temperature. Add mild soap, preferably, mild wool detergent or baby shampoo. Place your knitted jumper in the water and swirl around gently.

2-Rinse and drain the basin while gently pressing down on the knit to remove excess water, being careful not to wring or twist and change the shape.
 
3-Spread the jumper out on a thick, dry towel. Roll the towel with the sweater the way you would a yoga mat, pressing down as you go. Unroll, and lay your jumper down flat on the towel. Reshape, pushing ribbing together. After 12-24 hours, your knit should be ready to wear. If any wrinkles or folds remain, use a steamer.