How to get a PDM assigned to our company?

Microsoft will reach out to partners to assign a PDM once they reach a certain revenue and other metrics threshold. PDMs are only assigned to Managed partners. 

If a partner is managed, Microsoft will initiate contact and set objectives and partnership goals for the fiscal year, which begins in July. 

For unmanaged partners, several online resources are available, such as information repositories, document collections, and community calls. If you are not aware of these, start with the https://partner.microsoft.com/ (Especially the partnership menu) and https://learn.microsoft.com/partner-center/announcements/.

If you are a Direct Cloud Solution Provider (CSP) seeking technical advisory to support your business growth in the cloud, you might consider Microsoft's https://partner.microsoft.com/support/partnersupport, such as Advanced Support for Partners. FYI  these support plans primarily assist with technical enablement rather than programmatic aspects like the Microsoft AI Cloud Partner Program or Licensing programs.