In Reportz, you can apply custom filters in the Custom Filter field within a widget. 

Click on Add Data Widget and select Google Ads as Integration. 

After that, select your account and click on next.

In the second step, you can select your Ad account, Report Type, and choose your Widget. If you select any of the offered Report types other than Account Performance you could choose the Campaign and go below to Ad Set and Ad level.
These steps are entirely optional and you can leave each of those fields blank if you wish to.
Let's say that we want to filter out and show the data for only one of our conversions.
For this example, we will use a custom widget, and select Campaign Performance as the Report Type, Dimension (Click type), and Metric (All Conversions).

Below the widget, there is a custom filter field. Here we can filter our data using Google Ad's API.
For example, we would like to present only one conversion.
We can do this by filtering the conversions by the exact match name of the conversion click type. 

Since the click type dimension is of ENUM type we can find all possible values here

First of all, we need to see which conversions are listed. To do that, we first need to submit this widget, and then we will get a list of all the conversions that are available and the list looks like this. 

Let's say that we only want to show Sitelinks conversions. 

If you're using this exact match filter " == " it's very important to copy the exact name of the value you are looking for.

This is what the setup looks like. 

This is what the widget will look like after we apply the filter. 

Quick Pro Tip: if you want to filter out by the Dimensions and Metrics which are already in the widget, you can get their names by clicking on the Widget Details button. 

Afterward, just copy the entire name of the Dimension and Metric.

Nevertheless, you can filter out by any dimension and metric that's available so feel free to test it out. 

Here is a table with all the Google Ads operators that can be used in data Filtering.

NOTE: all text values in filters have to be wrapped by quotes " except predefined ENUM values.

To match a literal [, ], %, or _ using the =@ operator, surround the character in square brackets. For example, the condition
​campaign.name=@"[[]Earth[_]to[_]Mars[]]%"
will match all campaign.name values that start with [Earth_to_Mars].

Reportz Custom filter allows you to combine multiple filters for Google Ads using AND

Operators with () are used with multiple values which are separated by |, for example:

The AND operator is defined using a semi-colon (;), it CAN be used to combine dimensions and metrics in the same expression, for example: