OK, that makes more sense to me now that you say it is an Excel simulator.
The appropriate value to specify for an alt-specific attribute that doesn't apply to the current product concept is the same value that would have been coded during utility estimation for a not-applicable attribute. That is zero.
Be careful when using Excel simulators generated out of our software with linear terms; that the values going into the design matrix linear terms were automatically zero-centered when estimating utilities via CBC/HB or via Lighthouse Studio. So, you should continue to specify prices as zero-centered within your Excel simulator. If you fail to do this, it will throw off the proper estimation of the None %. The relative shares of preferences for the other product will be OK even if you've failed to do this.
For example, if you specified 1, 2, 3 for the prices for levels 1, 2, and 3 of a quantitative attribute (and you are using "Linear" coding rather than the default part-worth coding); our software automatically shifts those to -1, 0, +1 during utility estimation. Thus, to specify your product in an Excel simulator afterward requires using -1 to refer to level 1, 0 to refer to level 2, and +1 to refer to level 3. Otherwise, the None % will be wrong.