Italy to switzerland

3 days and 2 nights?
You can travel the Bernina Express route without using the Bernina Express train that has a 16EUR seat reservation fee. There are regular trains every hour.

Yes 3 days 2 nights. Kindly suggest the itinerary with travel guide.

Thanks in advance

We loved Interlakken.

Not sure if you want to spend time riding scenic trains through the mountains, or remaiming in one place for 2 nights and returning. I'll make a couple suggestions.

1. Train tour. Take train from Milano Centrale to Tirano, then train to St Moritz. Overnight in St Moritz. Next day take Glacier Express train to Zermatt. That is an 8 hour trip through the mountains east to west. The normal fare is 152 CHF plus 43 CHF seat reservation fee beginning May 30 (33 CHF before then). Here is how to save money on this trip. Buy a Saver Day Pass for 52 CHF up to 60 days before your travel date. The price of these goes up over time, so you need to buy early and be 100% certain you travel that day. It gives unlimited 2nd class travel throughout Switzerland for that day. You still have to pay the seat reservation fee. You can travel the same route without seat reservation fees if you take local trains, but you will have to change trains 4 times, at Chur, Disentis/Muster, Andermatt, and Brig. Next day, train back to Milan, via Visp or Brig.

2. Stay in a single place. Take train from Milan to Luzern. There is one direct train that you can buy advance tickets for 39 EUR now. It is nonrefundable, train specific, like an airplane ticket. It does use the new Gotthard base Tunnel, 50 km under the Alps. Stay 2 nights in Luzern. Return to Milan can be done with the Gotthard Panorama Express which begins with a boat ride on the lake to Fluelen. There you board a train to Lugano that goes mostly over the Alps with the old Gotthard tunnel, seeing all the scenery you missed on the way to Luzern. at Lugano, take next train to Milan.

There are any number of similar trips from Milan. Depends on your interests. Remember that Switzerland is expensive, much more so than Italy. Just be prepared for that.

And to the previous poster: what did you love about Interlaken? Most people who travel to that region love the things they see in the Lauterbrunnen Valley which is nestled in the alps and surrounded by snow capped peaks and the car free alpine villages...none of which is actually in Interlaken.

You say "I have nearly 3 days." (not even 3 complete days). In that time (2 nights), you only have time to visit one place in Switzerland.
How will you be travelling from Milan (train or car)? I am assuming train, as that is the most common method for tourists.

In which case I recommend somewhere in The Jungfrau region, either Mürren, Wengen, Lauterbrunnen or Grindelwald.
For info and hotels in these places see here: https://jungfrauregion.swiss/en/summer/

You can look up trains from Milan (Milano Centrale) to these places on the SBB website: https://www.sbb.ch/en

You do not have time for the Bernina line. To do that you need a multi-day tour of Switzerland stopping in many places.

Just noticed you posted: "Kindly suggest the itinerary with travel guide."
Hiring a guide in Switzerland is very very expensive.