Removing Outliers / Replacing

Good Day,

I do aplogize upfront to open a new topic but I failed to find a search function in the forum.

I have a simple question:

I have a wave from a measurement system which - sometimes if it is exposed to neaby high power electrical motors - creates fluctuating measurement values. 

They are obvious outliers and not related to a true measured value. See attached Graph1. 

I would like to do the below:

1) place my cursors at Start and End where the fluctation starts

2) replace (not delete them) the outliers (which are defined by the value < 3 in the example) by a given value; in the attached example by the value 3.431

The result should look like in "Graph2" below

I have played around with the ?: function, but was not successful, as I only could apply it to the entire wave and not to a certain part of the wave, given by the cursors. 

Thanks for your help,

Marc