First, get an overview of your expenses after retirement. Remember that some of these could increase, e.g., health, leisure, home repair/maintenance costs.
Your expected pension is made up of your AHV and pension fund pension. You can find the AHV pension in your AHV pension forecast, which you can order from your compensation office. As an alternative to an old-age pension, pension fund assets can also be withdrawn as a lump sum or as a mix of both lump sum and annuity. The amount of your assets is listed in your pension fund statement.
If the basic income is not enough, you should check what additional assets you have. These include real estate, securities, life insurance and assets held in pillar 3a.