(Please correct me if my reasoning is wrong somewhere)
Net Exports is a part of GDP and consequently its increase or a decrease also causes GDP to increase or decrease, assuming everything else stays equal. Higher import means lower Net Exports, while higher export means higher Net Exports.
Let's take two countries, country A and country C. Let's also assume that all internatinal trade happens between these two countries. If country C will increase its exports to country A, then GDP of country C, assuming everything else holds equal, will increase due to increased Net Exports part of its GDP equation. While for country A its GDP will decrease due to its decreased Net Exports.
From this it seems logical to conclude two things:
1.International trade is a zero-sum game from point of view of increasing/decreasing GDP.
2.If we want to increase our GDP, then among other things we must consider decreasing our import and increasing our export. For an example, we could outright ban some of foreign goods or raise tariffs, thus forcing our population to decrease consumption of foreign goods, this way increasing our GDP.
The only problem I see so far is that in the real world such policies can lead to trade wars, with other nations banning goods from our country and rasing tariffs on our goods, thus hurting our exports.