If the importer has requested a preshipment inspection, then now is the time to arrange for this to be done. Normally, the importer will have indicated the company or person that he/she wants to do the inspection. Obviously, you cannot contact the inspection company at the last minute and expect them to come at your convenience. Instead, you will have made arrangements well in advance (perhaps a week or two in advance) and you will keep them in the loop especially if you expect a delay to occur. A good relationship with this insepction company will bode well for your further relations with the importer. The inspection will need to take place before you pack the goods in the container. The inspection company may want to see actual products and you need to be ready to open up already closed packages that they may select at random in order to inspect the goods inside. These will need to be properly sealed again for shipment.
Bear in mind that some importers may require other forms of inspection and/or certification. For example, some importers may require tolerance tests, on-site inspections, destruction tests, or health certification (for certain foodstuffs, for example). These will have been spelled out in the L/C and you need to make the necessary arrangements for these inspections to take place and for the certification to be issued. The cost of these tests may be carried either by yourself or by the importer, but this, too, will be indicated (hopefully) in the L/C.