Get entries by custom matrix / date time field
I found the solution by using the following:

{% set startDate = now %}
{% set endDate = (now | date_modify("+2 months")) %}
{% set allTraining = craft.lowblocks.blocks.fieldId(72).type("trainingDateTimeDateTime").order("dateTimeFrom").limit(null) %}
{% set entryIds = [] %}
{% for course in allTraining %}
    {% if (course.dateTimeFrom &gt;= startDate) and (course.dateTimeFrom &lt;= endDate) %}
        {% set entry = course.owner %}
        {% set entryIds = entryIds | merge([entry.id]) %}
    {% endif %}
{% endfor %}
{% set entries = craft.entries.section("training").id(entryIds).fixedOrder(true).status("live,pending") %}